In typical prior isolating pressure sensors the pressure responsive element, e.g. pressure gauge, senses the pressure of the process fluid flowing in the line through an intermediary sensing fluid isolated from the process fluid by a resilient pressure transmitting member. Such isolating pressure sensors may be used, for example, where contact with the process fluid (e.g. an acid) would damage the pressure gauge. U.S. Pat. No. 3,163,529 and No. 3,563,095 disclose examples.
In one type of prior isolating pressure sensor for interposition coaxially between flanged ends of a coaxially opposed pair of pipeline sections, a U-shaped tube of resilient material contains the sensing fluid. A rigid body member interposed between the pipeline flanges has a bore coaxial with the pipeline. A circumferential, radially inward facing groove in the bore houses the hemicircular bight of the U-shaped tube. The ends of the tube extend tangentially from the bore through elongate parallel passages in an eccentrically extended portion of the body member and connect at the radially outboard end of the latter through fittings to a closable fill plug and a pressure gauge.
Several apparent problems are noted in prior systems of the latter type. Several factors tend to limit sensitivity, including exposure of the sensing fluid containing tube to less than the full circumference of the pipeline passage, location of a major portion of the sensing fluid tube out of contact with pipeline pressure, and (to limit the tendency of the bight portion of the tube to be swept from its groove by fluid flow through the pipeline) the desirability of relatively stiff tube material and of housing most of the cross section of the tube snugly within the groove and which tends to limit free expansion and contraction of the tube in response to changes in pipeline pressure. Also, such prior systems are complicated by the need for special connectors to connect the ends of the resilient tubing within the body member to rigid pipe fittings for the pressure gauge and fill plug. Further, substantial variations in pipeline pressure may tend to push and pull the tangential portions of the tube and cause same to creep axially, creating difficulty in maintaining a seal at the tube ends and in maintaining the tube bight portion in its groove at high process fluid flow rates. Further, although a circular cross section is compatible with conventional end connectors, such circular cross section is inherently more resistant to flexure of the tubing wall than would be a flat cross section, again tending to reduce sensitivity to small changes in pressure in the pipeline fluid.
A second type of prior isolating pressure sensor avoids some of the difficulties noted above, and provides an axially elongate body member of substantially U-shaped wall cross section having a cylindrical central portion terminating in radially outwardly extending end flanges. A resilient cylindrical member is coaxially spaced within the body member by an elongate annular sensing fluid chamber. Annular end plates coaxially fixed to the body member flanges axially press radially outwardly extending end flanges on the resilient member into corresponding, annular axially outward and radially inward opening reliefs at respective ends of the central portion of the body member for the purpose of sealing the ends of the annular fluid chamber. A pressure sensor of this latter kind is disclosed in aforementioned U.S. Pat. No. 3,563,095, assigned to the assignee of the present invention, and has been found to be generally satisfactory in use.
However, in a continuing effort to improve isolating pressure sensors, the present applicant has found that further improvement is possible, for example by reducing cost of and space required for the pressure sensor, particularly for larger diameter pipe systems, and in terms of positive securement of the resilient cylinder member.
Accordingly, the objects of this invention include provision of:
An isolating fluid pressure sensor for a pipeline in which a resilient cylinder, separating a surrounding sensing fluid space from process fluid flowing in the pipeline, has ends positively locked against inadvertent removal from the pressure sensor, even under difficult conditions, e.g. relatively high process fluid flow rates, changing and high process fluid pressures, use with thick or high friction process liquids, etc.
A pressure sensor, as aforesaid, which is compact in axial and radial thickness, and which can be securely sandwiched between end flanges of coaxially opposed pipe sections entirely within the confines of a standard flange bolt circle.
A pressure sensor, as aforesaid, in which the same pressure sensor unit may be used between various styles of pipe flanges without modification, despite substantial variation in bolt hole size, number and location, given correspondence in the internal diameter of the pipe flanges and the pressure sensor.
A pressure sensor, as aforesaid, which is of simple, economical construction.
A pressure sensor, as aforesaid, in which the pressure sensor can be stored and shipped precharged with sensing fluid without fear of leakage past the resilient cylinder, but wherein bolting of the pressure sensing unit between coaxial pipeline flanges tends to even more tightly seal sensing fluid and process fluid interfaces in the sensor.
Other objects and purposes of the invention will be apparent to persons acquainted with apparatus of this general type upon reading the following specification and inspecting the accompanying drawings.